Myths and Resolutions: You Don't Have To Drink 8 Glasses Of Water Every Day

Among the new year's resolutions that have been making the rounds this week, I've seen a few folks determined to drink more water.

For some reason, the "eight glasses a day" imperitive has sunk into the popular culture with the weight of religious doctrine. And nobody seems to know why.

The Eight Glass Debate In Class

I remember getting in a debate with my psychology teacher. For some reason she decided to lecture on the the importance of eight glasses a day. It probably had something to do with brain function.

In any case, I was mostly on-board with this regime. Rules and ritual make me feel comfortable. If a certain amount of water was going to improve my health, why not drink? And she was preaching with the certainty of a Catholic priest.

If I'm going to perform a ritual, though, I want to be sure I'm doing it right. So I raised my hand. "Does it matter how big the glasses are? Are we talking eight cups here, or eight pints, or something metric?"

"Well," she said, "you know, just eight good size glasses. Whatever size you'd normally drink."

"OK. So does it matter when I drink them? Every two hours? Every three? Should I be drinking now?"

It became apparent she hadn't thought about this very closely. "You should probably drink more in the morning. If you drink at night, you'll have to get up and go to the bathroom."

"But if I drink in the morning I'll have to ask for a hall pass during class."

She moved on, but something still troubled me. A few minutes later I raised my hand again. "Why does it have to be pure water?" I said. "If we drink juice or soda, it's still mostly water, isn't it?"

"Well, pure water is what your body needs. If you drink that other stuff, you've still got to drink the water."

"Another eight glasses."

"Yes."

"But what happens to the water molecules in a can of soda? Do our bodies throw them away? Do they disappear? Do the sugars and the carbonation just cancel the water out somehow?"

"That's it exactly!" she said, clearly relieved I'd provided an answer by asking my question in multiple-choice format. "It has to do with being all mixed together. If it's not pure water, your body can't use it."

You don't need to drink any particular amount of water to be healthy.

You could probably get by just fine without drinking any plain water at all.

20+ years later, I felt vindicated by reading *The First 20 Minutes: Surprising Science Reveals How We Can: Exercise Better, Train Smarter, Live Longer, by Gretchen Reynolds. This book looks at all kinds of health, exercise and performance myths, and examines what science has to say about them.

Obviously I was primed to absorb everything it had to say about water.

First of all, the water in coffee, tea, and soda does indeed count towards your daily needs. There's not even any truth to the corrolary myth that caffeine dehydrates you.

Even more interesting: most of the water we need in a given day (about a liter, on average) is supplied by our food! So while it's true that we dehydrate in a hurry if we don't get any water at all, it's also true that if we're eating, we're drinking.

Of course, vigorous exercise and heavy perspiration will dry someone out, increasing the need for water, right?

Well, sure. When you get to the end of that marathon, have a bottle of water. Or, as the Kenyans like to do, wait until the evening and drink several cups of weak bush tea with milk, to restore what you lost to sweat.

What you don't need to do is over-hydrate before a run. And you don't need to swill liter after liter of water during the course of it, either. Drinking too much during a marathon, actually, can kill you.

Should you deny yourself water? Of course not. Your body's thirst mechanism is precisely calibrated to keep your fluid levels balanced, and it's impossible to ignore.

Drink when you're thirsty. That's all that matters. You don't even have to think about it. Your body will tell you when it's time. I'll say it again:

As long as you drink something when you're thirsty, you'll be fine.

Is there any harm in drinking eight glasses of water a day?

Physically, not really. Your kidneys work a little harder and you spend more time going to the toilet.

If you drank much more than those eight glasses, you could upset the osmotic balance in your cells. This causes the "water intoxication," that kills those casual marathoners that stop for a drink at every aid station. (Interestingly, Reynolds pins some of the blame for these deaths on Oprah Winfrey, who popularized marathoning among her less-athletic followers after completing her first marathon in 1994.)

But if someone drinks eight glasses of water a day, and they say they feel better doing it, isn't that a good thing?

Habit formation and opportunity cost.

I don't know. To me, it sounds like a waste of good intentions.

Most people who resolve to drink eight glasses of water a day aren't going to keep that resolution. They're just never going to be that thirsty, and their bodies will, quite rightly, over-ride their arbitrary hydration schedule.

Maybe if they avoid all coffee, beer, wine, and soup; maybe if they restrict their diet to dry crackers and leathery meats - then, I bet, eight glasses of water might taste delicious.

But everyone else is going to miss that target, day after day, and feel guilty about it.

There are better things to feel guilty about.

It's hard to build good habits. It takes conscious effort applied over several months before a new skill or behavior feels like second-nature. If you form one new habit a year (on top of going to work, raising your kids, feeding the cat, and everything else you've got on your plate) you're doing great.

That's why it's so important to work on habits that are truly meaningful.

Trying to drink eight glasses of water a day, or even trying to drink more water than you feel like drinking, is a wasted opportunity.

Why not resolve instead to take the stairs instead of the elevator, or to read poetry for half an hour a day, or actually floss all of your teeth, or to say something kind to someone you love every morning.

Whatever's really important to you - focus on the love and let the water take care of itself.

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